Devices are known in the art which make provision for the recording, by means of decoders, of interactive programmes. The latter subsequently enable a user to interact, during the viewing of an application. For example, the document WO-01/50763 discloses the automatic recording of an auxiliary programme according to preset criteria, with a view to subsequent use by the user. Document WO-00/76213 relates to a prior recording of a software application, then of a television programme corresponding to the moment of its broadcasting, with appropriate markings for the interactivity relating to this application and the option for the user to trigger the interactive programme.
In interactive digital television systems, the broadcaster provides the terminal with a digital stream. This stream contains multiplexed data which make it possible to reconstruct the initial streams: for example video streams, audio streams, signalling data and interactive application.
For reasons of broadcasting cost and of downloading time, the broadcasters and providers of services tend to minimize the size of the applications. An effect of this is the non-existence of applications that contain additional content such as real-time video sequences enhancing broadcast programmes. Now, the use of these sequences may be very beneficial for the production of interactive adverts for example.
The prior downloading to the terminal of sophisticated applications can be envisaged, and may make it possible for data which it would be impractical, or even impossible, to download with the stream broadcast upon the triggering of an application to be made available locally. However, such an approach requires a coherent system that executes in a rather complex way, since it is necessary to organize a prior downloading of the applications into all the receivers concerned. In practice, receivers that have been unable to download the applications in the requisite time cannot benefit from the associated interactive services. Now, several factors might compromise the local availability of these applications: insufficient storage space, overly restricted bandwidth, failed prior connection to a network (for example the Internet) for downloading, etc.
Document EP-0989743 discloses a method of transmitting application data in a digital transport stream, these data relating to several services. An application data table, also transmitted, contains information about the applications transported in each service. This table enables in particular a decoder to decide whether or not to maintain applications when switching from one service to another (§[0148]), or whether download applications not yet present in the decoder but required by a new service (§[0121]).
Prior document WO-01/31920 describes a technique for managing multiple applications in a digital network, according to which a virtual application table (“VAT” table) is communicated to terminals. The latter are moreover furnished with authorization levels fixed by a multiapplications manager. On the basis of this information, each terminal is capable of constructing a local VAT table, which indicates those applications that the terminal must be furnished with, by downloading (p. 28, 1.3-27).
These latter two embodiments necessitate table tracking, management and utilization, which entails a relatively high level of complexity.
International application WO-00/64172 teaches a method for performing or otherwise a predefined action in a receiver, for example for selecting the display of information, as a function of the contents of triggers received by this receiver. This display is different depending on whether a predefined rule does or does not apply to the triggers received.
This technique requires that the management of the triggers be precisely coordinated with the chosen display schemes.
Patent US-2002/0059623 discloses a file system with dual mode in a television of a subscriber network. This system is designed to use local data when they are available and remote data (by downloading) in the converse case. The data required for services can be obtained beforehand by the receivers and be stored locally in the form of data relating to hyperlinks (§[0107]). Upon the execution of a corresponding service, a local application verifies the presence of these data in local memory and proposes to the user the execution of an improved version of the service using the hyperlinks (§[0109]).
Patent U.S. Pat. No. 5,966,120 describes a method for combining and distributing data with a pre-formatted real-time video. In a receiver, an augmented video programme is created by inserting selected portions of auxiliary data into a selected primary video programme. These auxiliary data may be stored beforehand in the receiver, so as to be utilized subsequently at the requisite time.
Prior document WO-02/32139 relates to systems and methods for providing media content on demand, for example on-demand video or audio content, or electronic publications. An interactive television furnished with appropriate means can retrieve further content corresponding to such selected media content, either at the same time as the latter is despatched, or by prior downloading (p. 42, 1.31-33). In the latter case, the interactive television is capable of also retrieving information associating the further content with the media content (p. 43, 1.9-14). The mode of display of the further content with respect to the media content may optionally be chosen by the user (p. 45, 1.4-7).
The potentialities of these latter three techniques remain restricted in practice to the displaying of small supplementary fields on the screen, added to the displaying of the base service, or to the introduction of sequences such as short advertising inserts.